The goal of the proposed research is to use new membrane potential probes we have developed in our laboratory to learn about early macromolecular and ionic events that take place in the retinal rod and disc membrane. We have developed a reconstituted rhodopsin-phospholipid vesicle preparation in which rhodopsin permits ion movements across the membrane following illumination. We want to determine the ion specificity of the rhodopsin channel and determine the effects of rhodopsin phosphorylation, temperature, vesicle lipid composition, and rhodpsin chromophore structure on the kinetics of the light gated rhodopsin permeability change. We plan to use our potential probes to determine the ion transport properties of disc membranes and rod outer segment plasma membranes. Finally, we want to develop highly sensitive membrane voltage probes that can be routinely used by neurophysiologists to study receptor potentials in visual systems where the use of microelectrodes is impractical.